The present invention relates to image forming apparatuses such as a both-surfaces copying machine for forming images on opposite surfaces of a sheet.
FIG. 16 shows a constitution of a conventional copying machine, that is, an image forming apparatus. In a copying machine 1, a sheet reversing section 200 for reversing a sheet 100 necessary for both-surfaces copying, and a stack cassette 300 for the both-surfaces copying are disposed. The stack cassette 300 is a storage section for temporarily storing the reversed sheet after an image is formed on one surface of the sheet during the both-surfaces copying.
An operation for the both-surfaces copying will be described below. When a copy button is depressed, the sheet 100 is supplied from a cassette 90, and guided to a photosensitive body 10 through a conveyance path 240. A toner image formed on the photosensitive body 10 is transferred to the sheet 100, and fixed onto the sheet 100 by a fixing unit 80. Thereafter, the sheet passes through a conveyance path 250, is then reversed by the sheet reversing section 200, and enters the stack cassette 300 for the both-surfaces copying.
When a desired number of sheets 100 are all taken in, the sheet 100 is taken out of the stack cassette 300, passed through a conveyance path 260, and fed to the photosensitive body 10. The toner image formed on the photosensitive body 10 is transferred onto a non-copied side of the sheet 100, and fixed onto the sheet by the fixing unit 80, and the sheet 100 having the opposite surfaces copied is discharged to a sheet discharge tray 2.
This constitution has the following problems.
Firstly, since the sheet reversing section 200 and stack cassette 300 for the both-surfaces copying are disposed in the apparatus, the entire apparatus has a large size.
Secondly, when the sheet is reversed, the sheet is passed through sharp corners (arrows 200a, 250a in the drawing) in the conveyance path of the sheet reversing section 200. Therefore, the sheet is bent, the load on the sheet being conveyed is enlarged, and a jam easily occurs.
An object of the present invention is to provide an image forming apparatus in which a jam in a conveyance path for reversing a sheet during both-surfaces copying is inhibited from occurring and in which the both-surfaces copying is enabled with a size of the entire apparatus being as small as possible.
In order to achieve the above object, according to one aspect of the present invention, there is provided an image forming apparatus including an apparatus main body having an image forming section, and a sheet discharge tray disposed outside the apparatus main body, the apparatus comprising: first image forming means which uses the image forming section to form an image on one surface of a sheet; a sheet discharge section for discharging the sheet with the image formed thereon by the first image forming means to the sheet discharge tray; a sheet supply section for supplying the sheet discharged to the sheet discharge tray by the sheet discharge section into the apparatus main body; and second image forming means which uses the image forming section to form an image on the other surface of the sheet supplied to the sheet supply section.
The sheet having the image formed on one surface thereof by the image forming section is discharged to the sheet discharge tray outside the apparatus. Thereafter, the sheet is supplied into the apparatus, and the image is formed on the other surface of the sheet by the image forming section. The image forming apparatus of the present invention does not include a stack cassette for both-surfaces copying and a sheet conveyance path having sharp corners inside the apparatus.